K click 8/8 I have a wire vs Low flying article

[revilla]

Update ...

 

Last night I got together with David Martin (GF04RCE on here) to have a good look at his car with the extra Brown/Blue wire on MFRU 8/8. His car had a very severe K-Click - it wouldn't actually start at all, even when cold, the solenoid just clicking loudly every time.

 

1) By tracing through with a multimeter we were able to confirm my suspicions from my earlier post that the extra Brown/Blue wire is the common +12V supply for all of the engine electrics such as injectors, coil packs etc. and that his car was wired pretty much in accordance with the original Rover wiring diagram (we used the MGTF for reference) and NOT as shown in the Caterham K-Series wiring diagram.

 

2) We were able to confirm that everything was happy if these were all converted to be connected directly to the ECU fuse rather than through the MFRU Main Relay, i.e. as is shown in the Caterham K-Series wiring diagram and as my car is wired.

 

3) We were able to confirm that the modification I described in the Low Flying article could be very simply adapted to suit cars wired in this way by simply splicing together the cut ends of the extra Brown/Blue wire from MFRU 8/8 and the unused Brown wire from MFRU 8/1, effectively converting the the engine electrics to work in the same way as in my car and in compliance with the Caterham K-Series wiring diagram.

 

As has been made clear many times by many people, the K-Click is a cumulative effect which may be caused by a combination of many factors. In David's car we found that his battery voltage was also low, reading 11.6V while energising the starter solenoid but not the motor itself - but it had been standing and he had been repeatedly trying to start the car for some time, so the battery was probably in a poor state of charge. There was also unacceptably high resistance somewhere in the wiring loom between the battery and the ECU fuse.

 

We found the high resistance initially by checking the voltage across the battery while under load energising the solenoid (11.6V) and the voltage across the solenoid itself (only 7.6V), leaving 4.0V dropped in the wiring somewhere. We then worked backwards systematically through the wiring looking for the point where the voltage dropped. Most of the voltage drop occurred between the battery and the live side of the ECU fuse, which should have just been wired directly together, however it did look as though the wiring loom on this car had been modified at some point and there were additional spade connector joints along the path of the main +12V feed wires from the battery which had been separated out from the loom where it ran across the back of the engine bay and spliced. I suspect that one of these joints was poor, probably dirty or corroded, although we didn't have the time available to work through every connector. Due to the low resistance and consequently high current requirement of the starter solenoid, only a small fraction of an ohm of extra resistance here (probably not even high enough to read directly on many multimeters) would introduce an unacceptable voltage drop.

 

To cure the above, we connected terminal 30 of the Starter Solenoid Relay not to the brown wire from MFRU 8/7 as described in my article (which had the high resistance) but through a new 30A in-line fuse directly to the battery +ve. Following this above, the car started easily, even on a poorly charged battery.

 

In David's case I suspect that this was actually the major cause of the problem rather than the MFRU relay, but as the MFRU relays are known to be a weak link I think it is still good that we were able to confirm that the fix described for the MFRU can be used in cars with this wiring.

 

I will update the instructions in my article to cover models wired in the same way as David's car and also add some instructions on how to track down and cure or work around poor wiring and high resistance. I will post an updated copy of the article here when I get a chance, but I will also see of Low Flying would be happy to publish a short update for the benefit of the whole community.

 

In the meantime if people with the extra wire want to go ahead and give my mod a try, you can follow the instructions in the article but use a crimp connector to splice together the Brown wire which I describe as unused and the extra Brown/Blue wire.

 

If people do give it a try, please feed back on here how it goes.

 

PS: For those who like technical reading, while trying to find specifications for the solenoid resistance and current drain on the Internet I came across this paper entitled "Starter solenoid and power contacts diagnostics" by J. POŠTA, R. PAVLÍČEK, T. HLADÍK of the Czech University of Agriculture, Prague, Czech Republic which interestingly uses the Skoda Felicia 1.3 starter motor as its example - which I believe is pretty much the same as the Caterham starter.

[Jonathan Kay]

Great fix, and a great explanation.

 

Well done.

 

Jonathan

[Mucus72]

Agree with Jonathan, great update Andrew! In fact I think it was Jonathan that mentioned in another recent post about the merits of some kind of wiki/blogging site that would allow the community to manage and create an everlasting series of "how to's" in the blended style of the FAQ section and the great (but not updated) Alcester Sevens site. Low Flying is the correct place in respect of print, but a more robust wiki series of articles that any of us could dip into for anything from servicing to fixes such as the K Click thread. If this was lightly curated it would be a magic resource.

 

And yes, I know...an indexed, searchable BlatChat can kind of get to the same result. But firstly you need to know what you are looking for, and sometimes you don't know what you don't know. Secondly the point of forums/twitter/chatter is to engage users in a stream on consciousness. Again, no good when you just want a solid set of wiki articles on K Click and you are up to your eyeballs in grease on the garage floor.

[GF04RCE]

What can I say.... but 😬 I have a car that starts and now know that i am dropping some volts in my wiring somewhere.

 

A big thanks to Revilla (Andrew) for all his hard work to come up with this fix, even for us in the Extra wire brigade... and also coming up with a solution for voltage drain in the loom with the direct feed. It was great of him to turn up last night to work it through... I also realised its time I bought myself a good set of crimpers and to throw my soldering iron away .....

 

Big Thanks again, and good luck to all those that make the relay swap.....

 

David M

[CliffC]

Andrew

 

Many thanks for this update and i look forward to your updated article.

 

Top job

 

Cliff

 

[MartinWoodham]

Mucus, great idea, already been done - it's called the 7FAQ

 

Revilla, thanks for the LF article, your posts here and your diligence in tracking k-click to earth 😬

 

A quick Q and some observations:

The LF article mentions the 'weak' relay - what do you mean by that?

 

On my own car, whenever I've had the click the car (and therefore starter & solenoid) has usually been hot, but not always. It's always been when the battery has been down a little.

 

I'd assumed that the click is the sound of the solenoid pulling in, and that therefore the starter relay is doing its job - but it sounds like there's a possibility of a 'weak pull' ie enough to click but not operate correctly?

 

From your solenoid voltage readings it sounds like a number of factors that in combination can cause the click:

1) relay/ wiring delivers a low voltage to the solenoid casuing click but insufficient pull-in to activate the starter

2) wiring losses give insufficient voltage at the starter itself to turn the starter motor over

3) starter/ solenoid resistance increased due to high temp

4) low battery combined with any or all of the above

[revilla]

Yes sorry when I said "weak" relay I was using pretty sloppy terminology, I was referring to the relay having increased contact resistance, possibly due to ageing, corrosion, burning etc. It only takes a tiny amount of extra resistance to lose a lot of voltage at the currents drawn by the solenoid, so for example only 0.1 ohms will drop 2 volts at 20 amps. As you rightly point out, this is cumulative and when added to any of the other factors you list may tip the balance. To your list I would also add increased mechanical resistance in the solenoid and starter mechanisms requiring a larger pull force and therefore current, possibly caused by wear, accumulated dirt or lack of lubrication. There are probably many other possible causes which we have not mentioned here. The performance of the starting system seems to be marginal at best and anything which degrades it's performance may contribute to the issue.